1. Field of the Invention
This invention relates to a head feeding apparatus and more particularly to a head feeding apparatus which moves a head for recording and/or reproduction in a direction of a diameter of a disk shaped recording medium by utilizing gears.
2. Description of the Prior Art
According to conventional art, an optical pickup device which is a recording and/or reproducing head is moved by a feeding apparatus in a direction of the diameter of a disk shaped recording medium such as an optical disk or optical magnetic disk at the time of recording or reproduction. This optical pickup device includes an optical pickup for reproducing information signals recorded in an information signal area of an optical disk and a base which carries the optical pickup and is movably supported.
The base is formed in a substantially rectangular shape and large enough for carrying the optical pickup. This base has guide shaft bearing portions in which a guide shaft described later passes through, the guide shaft bearing portions being disposed on both sides of the base and in a direction of the diameter of the optical disk.
A feeding apparatus for feeding this optical pickup device in the direction of the diameter of the optical disk includes a pair of the guide shafts for guiding the optical pickup device in the direction of the diameter of the optical disk and a moving mechanism for moving the optical pickup device in the direction of the diameter of the optical disk.
The pair of guide shafts are mounted on guide walls of the chassis such that they are apart from each other in parallel condition. Guide shaft bearing portions provided on the base of the optical pickup device pass through the pair of guide shafts. As a result, the optical pickup device is supported such that it is freely movable in a direction of the diameter of the disk.
The moving mechanism includes a rack mounted on one side of the base of the optical pickup device and a transmission mechanism which meshes with the rack to transmit a driving force from a driving motor.
The rack is formed in a rectangular shape having a vertically longer side extending in a direction of the diameter of the optical disk. The rack has a gear section along its moving direction, which is provided on one side thereof. The rack is moved together with the optical pickup device in the direction of the diameter of the optical disk.
As shown in FIG. 1, the transmission mechanism includes a first transmission gear 51 which meshes with a gear 54 of the rack 52 to move the rack 52, a second gear (not shown) which meshes with the first transmission gear 51 to rotate the first transmission gear 51 and a worm shaft (not shown) which meshes with the second transmission gear to rotate the second transmission gear. The worm shaft is fixed to a output shaft of a driving motor (not shown).
In the feeding apparatus for the optical pickup device having the above described structure, when moving the optical pickup device, the driving motor (not shown) is driven to rotate the worm shaft. This worm shaft rotates the second transmission gear (not shown). The second transmission gear rotates the first transmission gear 51. The rotated transmission gear 51 operates and moves the rack 52. If the rack 52 is operated, the optical pickup device is moved along a pair of the guide shafts. Depending on the rotation direction of the first transmission gear 51, the rack 52 moves the optical pickup device to the center of the optical disk or to the outermost peripheral portion thereof.
In the feeding apparatus for the optical pickup device described above, if the driving motor is driven suddenly, a sudden transmission force is applied to the rack 52 through the second transmission gear (not shown) and the first transmission gear 51 by a driving force of the driving motor. Because the rack 52 is fixed on the base of the optical pickup device, the optical pickup device is moved rapidly. Thus, conventional feeding apparatuses have a problem that the optical pickup device may strike the guide wall of the chassis.
Because the rack 52 is fixed to the base of the optical pickup device, when the rack 52 meshes with the first transmission gear 51 as shown in FIG. 1, there may occur a backlash 55 which is a gap along a pitch circle between the gear section 54 of the rack 52 and the teeth 53 of the first transmission gear 51. Thus, there is a problem that transmission efficiency may drop when the teeth 53 of the first transmission gear 51 applies a transmission force to the gear section 54 of the rack 52 in the feeding apparatus shown in FIG. 1.
If the optical pickup device is moved to the innermost peripheral portion or the outermost peripheral portion of the optical disk, it strikes the guide wall of the chassis and stops. At this time, because the rack 52 is fixed to the base of the optical pickup device, if a driving motor (not shown) continues to rotate, an excessive transmission force is applied to the rack 52 through the second transmission gear and the first transmission gear 51 by a driving force of the driving motor. As a result, in the feeding apparatus shown in FIG. 1, the gear section 54 of the rack 52, the teeth 53 of the first transmission gear 51 and the teeth of the second transmission gear may be damaged.
In the apparatus shown in FIG. 1, if the driving motor is stopped, the rack 52 is stopped through the second transmission gear and the first transmission gear 51. Because the rack 52 is fixed to the base of the optical pickup device, if an external force is applied to the optical pickup device, the rack 52 is about to be moved together with the optical pickup device. At this time, the gear section 54 of the rack 52 applies a load to the teeth 53 of the first gear. Consequently, the feeding apparatus shown in FIG. 1 has a problem that the gear section 54 of the rack 52, the teeth 53 of the first transmission gear 51 and the teeth of the second transmission gear may be damaged.